Optical integrated circuits (OICs) come in many forms such as 1×N optical splitters, optical switches, wavelength division multiplexers (WDMs), demultiplexers, optical add/drop multiplexers (OADMs), and the like. Such OICs are employed in constructing optical networks in which light signals are transmitted between optical devices for carrying data and other information. For instance, traditional signal exchanges within telecommunications networks and data communications networks using transmission of electrical signals via electrically conductive lines are being replaced with optical fibers and circuits through which optical signals are transmitted. Such optical signals may carry data or other information through modulation techniques, for transmission of such information through an optical network. Optical circuits allow branching, coupling, switching, separating, multiplexing and demultiplexing of optical signals without intermediate transformation between optical and electrical media.
Such optical circuits include planar lightwave circuits (PLCs) having optical waveguides on flat substrates, which can be used for routing optical signals from one of a number of input optical fibers to any one of a number of output optical fibers or optical circuitry. PLCs make it possible to achieve higher densities, greater production volume and more diverse functions than are available with fiber components through employment of manufacturing techniques typically associated with the semiconductor industry. For instance, PLCs contain optical paths known as waveguides formed on a silicon wafer substrate using lithographic processing, wherein the waveguides are made from transmissive media including undoped silica, doped silica and glass, which have a higher index of refraction than the chip substrate or the outlying cladding layers in order to guide light along the optical path. By using advanced photolithographic and other processes, PLCs are fashioned to integrate multiple components and functionalities into a single optical chip.
Optical tap(s) are employed, for example, to monitor signal(s) carried in a waveguide. As illustrated in FIG. 1, a conventional optical tap OIC 100 includes a base 104, such as a an undoped silica film, with a source input port 102, a source output port 106 and a tap output port 124. A multiple wavelength light input signal is received at the source input port 102 (e.g., from an optical fiber in a network, not shown) and transmitted across the OIC via a source waveguide 110. A tap waveguide 122 is parallel to the source waveguide 110 for a length L in a coupling region 120. Thereafter, the tap waveguide 122 is offset and/or tapers away from the source waveguide 110. Through optical coupling in the coupling region 120, the tap waveguide 122 carries an output signal to the tap output port 124 that is based on the input signal. However, power is undesirably wasted (e.g., up to 2 to 3 percent) in the tapping process.